Embodiments of the present invention relate to an anti-fuse circuit and an integrated circuit (IC) including the same, and more specifically, to a technology for use in all kinds of semiconductor devices or system ICs, each of which includes an anti-fuse circuit using a breakdown phenomenon of a gate oxide, which is capable of preventing the occurrence of an anti-breakdown phenomenon of the gate oxide in the anti-fuse circuit.
Semiconductor devices cannot be used as memory devices when a defect or failure occurs in at least one unit cell therein during a fabrication process. The memory device having at least one failed unit cell is classified as a defective product, and results in decreased production efficiency.
Therefore, a technology has been introduced for substituting a defective cell with a redundancy cell included in a memory device so as to restore the memory device, which increases the production yield and reduces production costs.
A repair task of substituting the defective cell with the redundancy cell is designed to use a redundancy row and/or a redundancy column formed in every cell array, such that the row or column including the defective memory cell is replaced with the redundancy row or redundancy column.
For example, if a defective cell is detected in a test process after the fabrication process is finished, a program operation for making access to a redundancy cell with an address input to access to the defective cell is carried out in an internal circuit of the memory device.
Therefore, if an address signal corresponding to a defective line used to select the defective cell is input to the memory device, a redundancy line used to select the redundancy cell is accessed instead of the defective line.
A typical repair process is designed to use a fuse. The fuse-based repair process uses fuses built in the internal circuit to repair the defective cell, and applies overcurrent to a specific fuse located at a line coupled to the row or column including the defective cell such that the specific fuse is blown.
In addition, in order to replace the row or column including the defective cell with the redundancy row or redundancy column, the above-mentioned repair process may use a variety of methods including a method for burning off a fuse with laser beams, a method for interconnecting junction parts with laser beams, and a method of using the EEPROM programming.
From among the above-mentioned methods, the method for burning off the fuse with laser beams is considered the simplest and most reliable method and has the lowest probability of causing wrong programming. As a result, it has been widely used. In this method, a fuse is made of polysilicon or metal.
However, since the method for repairing a semiconductor device using a fuse performs the repair process on a wafer level, it cannot be applied to a packaged semiconductor device. Therefore, a new method to overcome the limitations of the above-mentioned repair method using an anti-fuse is introduced.
The method using the anti-fuse can perform a program capable of easily repairing a defective cell, even if it is included in the packaged memory device. The anti-fuse performs the opposite function to the fuse. That is, the anti-fuse starts with a high resistance, e.g., 100 MΩ and is designed to create an electrically conductive path, whereas the fuse starts with a low resistance, e.g., less than 100 MΩ and is designed to break an electrically conductive path.
Generally, the anti-fuse is formed with a very thin dielectric material of a non-conducting amorphous material, e.g., SiO2, silicon nitride, tantalum oxide, or ONO (silicon dioxide-silicon nitride-silicon dioxide) between two electrical conductors.
In other words, the anti-fuse is configured by forming a gate oxide between a silicon active region and a gate electrode. The anti-fuse may have the same structure as that of a transistor, widely used as a semiconductor device. The anti-fuse may or may not include a source/drain region as necessary.
In accordance with a programming operation of the anti-fuse, a predetermined voltage (program voltage, for example, 10V) is applied to the anti-fuse during a sufficient period of time such that the dielectric material located between two conductors is broken down to program the anti-fuse. Therefore, if the anti-fuse is programmed as described above, the two electrical conductors of the anti-fuse short-circuit, such that the anti-fuse has very low resistance.
As described above, the anti-fuse can be easily programmed and has a substantial difference in resistance before and after the programming operation. As a result, the anti-fuse has been widely used in semiconductor devices, for example, field programming gate array (FPGA), programmable read only memory (PROM), programmable array logic (PAL), etc.
From among various anti-fuses, FIG. 1 illustrates a MOS-type anti-fuse that is comprised of one MOS capacitor MC1 in which a source and a drain of an NMOS transistor are coupled to each other. While the MOS-type anti-fuse is programmed, a high program voltage Vpgm, which has a voltage level equal to or higher than that of an operation voltage, is applied to a gate electrode of the MOS capacitor MC1 such that a gate oxide film is broken down.
In other words, the program voltage Vpgm causes breakdown of a dielectric material. This electrical short-circuited status is considered a programmed anti-fuse.
If the anti-fuse is programmed, in order to read out information stored in the anti-fuse, a read voltage Vread is applied through a read circuit to determine whether the anti-fuse is opened or short-circuited. However, when repeatedly performing the read operation on the anti-fuse, an anti-breakdown phenomenon may occur in the anti-fuse by electrical stress caused by the read voltage Vread. This means that the breakdown of the dielectric material may be recovered, such that the resistance status of the anti-fuse may be changed. Thus, information stored in the anti-fuse may be also changed.
In this case, the program voltage Vpgm and the read voltage Vread are provided through a driver D1. The program voltage Vpgm may change depending on the thickness of the gate oxide film.
If the single MOS capacitor MC1 is used as the anti-fuse, it is difficult to acquire uniform breakdown characteristics. That is, the breakdown of an oxide film occurs in a weak point of the oxide film. However, since such weak points of respective fuses are different in distribution and range, the individual fuses, whose dielectric material has been broken down, may have a different resistance from each other.
Further, provided that soft breakdown instead of hard breakdown occurs, resistance after soft breakdown increases, so that the anti-fuse programming may not be achieved normally, resulting in the occurrence of errors.
FIG. 2 shows an anti-breakdown phenomenon occurring in a general anti-fuse circuit.
The dielectric material in the anti-fuse circuit, which is broken down by the program voltage Vpgm, may be recovered by the anti-breakdown phenomenon caused by a voltage supplied in a subsequent repeated read operation.
The anti-breakdown phenomenon may unexpectedly reverse the program status of the anti-fuse. In this case, the anti-breakdown phenomenon may occur by a current flowing through the short-circuited anti-fuse.
As shown in the graph of FIG. 2, the breakdown phenomenon and anti-breakdown phenomenon may be repeated in response to a voltage applied to a gate electrode of the anti-fuse.